According to the Myth of Er we are responsible for our character because we chose it before birth. But any choice is determined by our present character, sothere is an indefinite regress and we cannot be entirely responsible for our character. The Myth of Er can be seen as the first formulation of the problem of free will, which Aristotle demythologizes in Nicomachean Ethics III.5. Plato's solution is that freedom is compatible with causal determinism because it does not mean indeterminism but rationality. The myth links the individual lives to the harmony of the spheres, so our lives are determined not by blind necessity, but by rational necessity that follows from the nature of the universe. Even so, the limitations of determinism prevent rationality from being a sufficient cause of happiness (although the opposite view is usually attributed to Plato), but it remains a necessary one